ESPN on Thursday ended its official association with "Frontline," the public television public affairs series, on a two-part documentary about concussions in the NFL that is scheduled to be televised in October. After 15 months on the venture, ESPN chose to strip its name, logo and credit from the films, "League of Denial: The NFL's Concussion Crisis."

ESPN belatedly focused on the fact that it did not have editorial control of what appeared on "Frontline" long into a collaboration that has already resulted in nine joint television and online reports that have appeared on ESPN's "Outside the Lines" program, on ESPN.com and on the "Frontline" website. Together they also created Concussion Watch, a database that tracks concussions and other head injuries in the NFL.

Chris LaPlaca, an ESPN spokesman, said, "In hindsight, we should have reached this conclusion much sooner."

But Raney Aronson-Rath, the deputy executive producer of "Frontline," said that ESPN executives had for more than a year understood the ground rules of the collaboration: "Frontline" would keep editorial control of what it televised or put on its websites, and ESPN would have control of everything it televised or posted on the Web.

"We were about to share a cut of our film with them," Aronson-Rath said, "and we welcomed their input."

But ESPN would not continue with the venture with "Frontline," which has won 15 Peabody Awards.

In a statement, ESPN said: "Because ESPN is neither producing nor exercising editorial control over the 'Frontline' documentaries, there will be no co-branding involving ESPN on the documentaries or their marketing materials. The use of ESPN's marks could incorrectly imply that we have editorial control."

ESPN added that it would still "cover the concussion story through our own reporting."

LaPlaca said ESPN's decision was not based on any concerns about hurting its contractual relationship with the NFL.

Last Sunday, "Outside the Lines" carried a critical report as part of its "Frontline" collaboration about Dr. Elliot Pellman, a former chairman of the league's research committee on concussions whose qualifications for that position were questioned. He resigned in 2007.

Even with ESPN no longer identified as a collaborator on the "Frontline" films, they will retain a clear ESPN flavor because they are heavily based on the reporting of Steve Fainaru and Mark Fainaru-Wada, brothers and investigative reporters for ESPN. They are the authors of a book, "League of Denial: The NFL, Concussions and the Battle for Truth," which is to be published Oct. 8.

The documentaries will run on Oct. 8 and 15.

"We're obviously disappointed because the partnership has been a phenomenal one and we don't totally understand what happened," Fainaru-Wada said. Referring to ESPN, he added, "Nothing we've been told by anybody suggests that they're backing off on the journalism."

Aronson-Rath said that until last Friday, there had been no hint of trouble between "Frontline" and ESPN. She said that "Frontline" had worked "in lockstep" with Vince Doria, ESPN's senior vice president and director of news, and Dwayne Bray, senior coordinating producer in ESPN's news-gathering unit.

But in conversations last Friday and on Monday with Doria and Bray, she was first told that ESPN did not want its logo to be connected to the films, and on Monday that they wanted to remove ESPN's credit as a collaborator.

"It didn't appear that it was their decision," she said.

Aronson-Rath said that the Fainaru brothers started working with "Frontline" before ESPN was asked to collaborate.

"The response we got from them was terrific and everyone was very excited," she said.

The NFL was not supportive of the documentary.

Greg Aiello, a spokesman for the league, said it declined to make Commissioner Roger Goodell and other executives available for it.

"Frontline" has interviewed several doctors who advise or have advised the league, but Aronson-Rath said three members of the NFL's head, neck and spine committee had recently agreed to on-camera interviews before canceling them.